Because the laser beds are manufactured from aluminium they are by nature heat conductors. Flashback is caused when the laser meets any metal element of the cutting bed on the reverse of the material as it slices through. This can result in very small nicks from the underside laser cut edge. Flashback is most common on materials thicker than 5mm particularly acrylic as it is brittle.
In all cases we try to keep flashbacks to a minimum. All our laser settings are configured to an optimum power to minimize damage. We try to avoid using honeycomb where possible and use lamella slats but in some cases if your artwork is particularly dense, we need to use it to maintain support which can result in flashback.